The present invention relates to analog-to-digital converter (ADC) apparatus; and more particularly, it relates to switched-capacitor circuit ADC apparatus.
Switched-capacitor (SC) circuit technology is finding application in the field of data acquisition, particularly as applied to analog-to-digital conversion. For example, in McCharles et al., "An Algorithmic Analog-to-Digital Converter", IEEE Int'l Solid-State Circuits Conf. Digest of Tech. Papers (1977), pp. 96-97, there is described an iterative type A/D converter implemented in SC circuit technology. The apparatus described by McCharles et al. utilizes ratioed capacitors to provide the "times two" function required to implement the successive-approximation algorithm for converting an analog voltage to a multiple bit digital word. Errors in the capacitor ratio produce nonlinear distortion in the transfer function upon reconstruction of the analog signal from the digital words produced by the converter. The nonlinearity can, of course, limit the conversion resolution of the converter.